1. Technical Field
The present invention relates to an optical film useful for liquid crystal display devices or the like, and to a retardation plate, elliptical polarizing plate and liquid crystal display device having the same. The present invention relates also to compounds which are useful for producing optical films.
2. Background Art
It is known that discotic liquid crystal compounds are important as a material for optical compensation sheets. Examples of a liquid crystal compound exhibiting a discotic liquid crystallinity include 2, 3, 6, 7, 10, 11-hexa {4-(4-acryloyloxyhexyloxyl)benzoyloxy}triphenylene (for example, JPA No. 8-50206).
Usually, retardation, Δnd, of an optical compensation film may be determined depending on the optical properties of a liquid crystal cell to be compensated by the film. Retardation of an optically anisotropic layer, Δnd, is a product of birefringence, Δn, of the layer and the thickness, d, of the layer. Even if the layer is thin, the layer, having large birefringence, Δn, would be able to compensate birefringence of a liquid crystal cell. On the other hand, the layer having small birefringence, Δn, wouldn't be able to compensate birefringence of a liquid crystal cell unless the layer is thick. Forming a thick layer containing aligned liquid crystal molecules suffers from more defections in the alignment compared with forming a thin layer containing aligned liquid crystal molecules. Therefore, compound having higher Δn may be more useful for producing optically anisotropic layers or the like.
In JPA No. 2007-2220, compounds having high Δn are disclosed.
In JPA No. 2007-204705, liquid crystal compounds, having a skeleton similar to that of the compounds disclosed in JPA No. 2007-2220 and two side chains, are disclosed.